1. Field of the Invention
The present invention relates to an impact sensor which detects that each of accelerations of set acceleration thresholds in magnitude has just acted and a method for manufacturing the impact sensor.
2. Description of the Related Art
In a conventional impact sensor, a first substrate where is formed a cantilever beam having a flexible portion whose one end is fixed to a frame-like support and at whose free end a mass portion is formed, a second substrate on which is formed a first electrode facing a second electrode formed on the mass portion, and a third substrate on which is formed a fourth electrode facing a third electrode formed on the mass portion are laid one over another via a glass layer to form a unit, and the length, width, and thickness of the flexible portion are changed to adjust sensitivity in acceleration detection. A plurality of the units are arranged to detect a plurality of acceleration thresholds. Refer to Japanese Patent Application Laid-Open Publication No. H10-68742 (Reference 1).
There is another device where an annular magnet movably supported by a coil spring and a pair of reed switches having respective contacts located at different positions along the movement direction of the annular magnet are arranged inside a cylindrical tube to form an impact sensor. One or both of the reed switches become closed depending on the position of the magnetic field associated with the annular magnet that moves against the biasing force of the coil spring due to acceleration that varies in magnitude, and thereby different acceleration thresholds are detected. Refer to Japanese Patent Application Laid-Open Publication No. 2002-48814 (Reference 2).